Chicago, July 5 (Reuters): Smoking a water-pipe or hookah may be chic, but the carbon monoxide, nicotine, tar and heavy metals contained in the smoke pose often-ignored health threats, researchers said today.

The concentration of cancer-causing and addictive substances in tobacco blends smoked in water-pipes can be higher than those found in cigarettes, according to a report published in the medical journal, Pediatrics.

Common for centuries in the Arabian Peninsula, Turkey, India, Pakistan and some regions of China, water-pipe smoking had been in decline in the past century and principally become a habit of older men in bazaar cafes.

But the report cited an upsurge in hookah smoking in recent years with “hookah bars” in major cities.

It estimated that more than 100 million people globally smoke a water-pipe on any given day.

“This phenomenon has been attributed to the perception that water-pipe smoking is less dangerous than cigarette smoking, its easy availability, its low cost, and a number of other factors,” wrote report author Barry Knishkowy of Israel’s ministry of health in Jerusalem.

In Israel, sharing a water-pipe is a way for the nation’s Jewish and Arab youth to mesh two cultures, and a survey of 6,000 teenagers found 40 per cent of Jews and 31 per cent of Arabs had smoked a water-pipe.

The tobacco used in hookahs comes in three forms: maasel contains tobacco mixed with honey or molasses, tumbak or ajami is pure tobacco paste, and jurak usually contains fruits or oils. Some smokers add alcohol, hashish or marijuana.

Carbon monoxide concentrations found in the bloodstreams of water-pipe smokers has been found to be quadruple the levels in cigarette smokers, the report said.

The nicotine content in water-pipe tobacco also tends to be higher than that found in cigarettes. However, pipe smokers are less likely to make it a daily habit.

Studies have shown lung and bladder cancer rates are higher among water-pipe smokers than among nonsmokers, and they are also at risk from pulmonary disease and other types of malignancies, the report said.

A study of Egyptian couples found an association between water-pipe smoking and infertility, it said.

Water-pipe or hookah smoking is known by various names including narghile, aggileh, goza, hubble-bubble, and shisha, and was believed to have originated in India.

It is relatively inexpensive and many believe it lacks the unhealthy stigma sometimes associated with cigarettes, thinking wrongly that the water-cooled smoke has fewer unhealthy ingredients.

The report urged health authorities to monitor the incidence of water-pipe smoking and regulate the content of the substances smoked.

It also suggested providing disposable nozzles to lessen the spread of infections.

“Health education is important to dispel myths about Narghile’s alleged safety,” it said.